1. Field of the Invention
The present invention relates to a magnetic disc apparatus, and more particularly to a magnetic head moving apparatus which sends the magnetic head in a prescribed direction by moving it.
2. Description of the Prior Art
The principal part of the magnetic head moving apparatus which is currently in the widest use in magnetic disc devices has a construction as shown in FIG. 1 and FIG. 2.
Namely, a magnetic head 101 is fixed via a flexer 102 to a head stand 103, and the head stand 103 is fixed by guides 104 and pulleys 105 to a carriage 106 which is supported so as to be movable only in the direction A (the radial direction of the magnetic disc) in the figures. On the carriage 106 there are fixed both ends of a flexible band 110 whose central portion is wound and fixed to the periphery of a roller 109 that is fitted to the shaft 108 of a stepping motor 107.
Because of such a construction, by rotating the stepping motor 107, it is possible to move the carriage 106 in parallel in the direction A of the figure for a distance which is proportional to the angle of rotation of the motor. In order to enhance the positional accuracy of the magnetic head 101 by fixing the flexible band 110 to the carriage 106 without sag, a method has been employed in the past in which a fixed tension is given to the flexible band 110 by fixing it to the carriage 106 via a punched rectangular elastic member 111 that is provided on one end of the flexible band 110.
However, in a magnetic head moving apparatus with the construction as in the above, the flexible band 110 is to be fixed via the elastic member 111 to the carriage 106 with screws or the like under a strained condition so that it requires special fixing tools and it used to deteriorate the workability. Moreover, it used to be not easy to fix the flexible band 110 under appropriate tension because of the twist in the flexible band 110 at the time of its fixing with screws or of the change in the tension after fixing, that tend to be generated.
Furthermore, in a magnetic head moving apparatus constructed as in the above, the accuracy of setting in the direction of height, as shown by the direction B in FIG. 2, of the flexible band 110 depends upon the manufacturing accuracy of the carriage 106 and the form accuracy of the elastic member 111, so that it was not possible to eliminate the errors in the height of setting because of the errors in the accuracy of these members.
Still further, the attached position, on the roller 109, of the flexible band 100 does not change so that in winding the flexible band 110 on the roller 109, the roller 109 necessarily moves relatively in the horizontal direction. In this case, if the flexible band 110 is set with some error in its height and is slightly tilted instead of being perfectly horizontal, the length of the flexible band 110 is changed by expanding or contracting the elastic member 111, depending upon the position of the roller 109 and the carriage 106. In practice, the flexible band 110 has to have a larger length when it is in the vicinity of the end of the carriage 106 than in the case when it is in the vicinity of the center of the carriage 106, with an expansion of the elastic member 111 and a corresponding change in the tension. Because of this change in tension, the feeding accuracy of the magnetic head 101 will deteriorate.